Vessel with rotatable pod

ABSTRACT

A vessel and a method for driving a vessel. The vessel is provided with a pod arranged at the rear side thereof which is arranged rotatably with respect to the vessel. Rotation is effected about an axis which deviates slightly from the vertical. The axis of the propeller shaft forms an angle which is smaller than 90° with the axis of rotation of the pod. As a result of this combined positioning of the rotation shaft of the pod and the positioning of the propeller shaft, the axis of the propeller shaft with respect to the horizontal will vary when the pod is rotated depending on the rotation position of the pod. This permits optimum adaptation to the various operating conditions of the propeller position.

FIELD OF THE INVENTION

The invention relates to a water-displacement vessel comprising a hullwith a longitudinal axis, comprising a bottom and comprising a pod drivearranged close to the bottom, said pod drive being provided with ahousing containing a propeller shaft which protrudes through the housingand to which propeller shaft a propeller is attached at a propeller end,and a drive for said propeller shaft, which propeller shaft defines afirst axis, which housing is rotatable with respect to the hull betweena rearward position and a forward position about a rotation shaft whichdefines a second axis which is not vertical and forms an angle (α) of40°-90°, preferably between 60°-80°, with the first axis.

More particularly, the present invention relates to relatively largevessels, i.e. vessels having a length of more than 20 metres and inparticular more than 50, or even more than 80, metres and having a waterdisplacement of 500 tons or more. The invention also relates to a methodfor the propulsion of vessels of this type.

BACKGROUND OF THE INVENTION

A pod drive is a more attractive alternative to a conventional drivewhich uses a propeller shaft in a fixed position with respect to thevessel, to which propeller shaft a propeller is attached, and which usesa rudder for manoeuvring. In particular when using electrically drivenpods, it is possible to provide diesel-electric propulsion which can beoptimized depending on the operating conditions. By using a number ofunits to generate electricity, it is possible to increase theoperational reliability and also the efficiency. It is also possible,depending on the position, to comply with current regulations, such asenvironmental regulations.

A water-displacement vessel according to the preamble of Claim 1 isdescribed in GB 2 009 156, wherein two Voith-Schneider propellers areattached under respective hulls of a vessel designed as a catamaran,comprising a propeller and optionally a casing. The rotation shaft ofthe suspension of the propellers is at an angle with respect to thevertical. As a result, during rotation into a sideward position, forexample during manoeuvring, the propellers can be directed obliquelydownwards and obliquely upwards in such a way that the resulting flow ofthe propeller on one hull does not disrupt the operation of thepropeller of the other hull. In the straight-ahead position, therotation shafts of the propellers are parallel to the longitudinal axisof the vessel.

In order to achieve sufficient buoyancy, the known vessel has a depthwhich is such that the propellers are at all times situated sufficientlyfar below the surface of the water to have a good propulsive effect.

U.S. Pat. No. 3,306,246 discloses a planing vessel, wherein a propellerarranged at an angle raises the hull out of the water in a rearwardposition and pulls the hull into the water in a forward position,without a hydrofoil being necessary for this purpose.

In other vessels known from the prior art, the axis of the propellershaft is perpendicular to the axis of rotation of the pod housing withrespect to the vessel. In addition, the second axis, i.e. the axis ofrotation of the pod housing with respect to the vessel, is vertical. Inthis way, the horizontal position of the first axis, i.e. the axis ofthe propeller shaft, is always ensured when the housing is rotated withrespect to the vessel. This position is optimum for driving the vesselover relatively great distances.

Although, in theory, a horizontally arranged propeller shaft offers theoptimum thrust for propelling a ship, in specific cases the designer maychoose to set the propeller shaft at a (slight) angle in sailingconditions, for example parallel to the flow along a hull shape.

If a vessel of this type makes a round trip where little or no load ispresent, it is necessary to provide said vessel with ballast. If nomeasures were taken, the relatively low weight would cause the vessel toride higher and would lead to conditions which are no longer optimum forpropulsion by means of the propeller.

Conversely, it has been found that if the surface area or the volume ofthe vessel which is in contact with the water decreases, the flowresistance decreases, as a result of which it is possible to sail eitherat increased speed or with lower consumption.

It is the object of the present invention to provide a vessel which hasoperating conditions in the loaded state which are comparable to thoseof a conventional vessel known from the prior art. However, theintention is to further improve the operating conditions of the vesselin a state in which the vessel is less loaded.

It is a further object of the invention to provide a water-displacementvessel comprising a rotatable pod which is suspended by means of arotation shaft arranged at an angle with respect to the vertical, withit being possible to propel said vessel in an effective and efficientmanner both with a large draught and a relatively small draught.

SUMMARY OF THE INVENTION

In a vessel of the type described above, this object is achieved byvirtue of the fact that an annular jet pipe is arranged around thepropeller, comprising a peripheral edge which is at a distance from thepropeller shaft and is situated further below a predetermined waterlinein the forward position than in the rearward position, wherein thedirection of rotation of the propeller shaft in the forward position isadjustable in such a way that the jet pipe has a water-suction effect.

As a result of the non-vertical placement of the second axis incombination with the non-perpendicular positioning of the first axiswith respect to the second axis, in the case of rotation about thesecond axis the first axis will always be moved into a differentposition with respect to the horizontal (and the vertical) depending onthe rotation. In the simplest embodiment, the first axis, i.e. the axisof the propeller shaft, defines a cone during rotation about the secondaxis, i.e. the axis of rotation of the pod. More complicated movementsare also possible. This enables the position of the axis of thepropeller shaft to be adjusted depending on the rotation position of thehousing of the pod. In other words, in a drive position, or rearwardposition, said axis of the propeller shaft is preferably in the usualhorizontal position. However, following rotation through 180° into theforward position of the pod, the axis of the propeller shaft will form aconsiderable angle with the horizontal. As a result of this tilting ofthe propeller shaft and thus of the propeller, the depth of the inlet ofthe annular jet pipe under the surface of the water increases withrespect to the vertical, since it receives a horizontal component. Theupper side of the peripheral edge of the jet pipe therefore lies deeperin the water in the forward position and is able to suck in this water,without a disruptive amount of air being sucked in during the process.

It has been found that this enables, inter alia, a vessel provided withlittle or no ballast ballast to be driven. The starting point is theposition described above in which the propeller and the jet pipe areinclined with respect to the horizontal. As a result of the incline, thepropeller and the inlet of the jet pipe are in a position in which theydo not protrude above the surface of the water, which would risk thesuction of air. The rotation of the propeller is then started and thevessel is driven. In this case, the propeller rotates “in reverse” inorder to suck water into the jet pipe and to move the vessel forwards.The non-horizontal position means that the efficiency of the drive isless than when the propeller is in the horizontal position. However,this operation is temporary. As soon as the vessel has gained somespeed, a stern wave will arise and the propeller can once again bepositioned such that the propeller shaft is substantially horizontal.The propeller then rotates “forwards” again in order to move the vesselforwards.

The design of the pod is not relevant to the present invention. That isto say that the pod may either have an engine located in the vesselwhich drives the propeller shaft in the housing by means of a shaft andgear wheels, a thruster, or may be provided with an (electric) motorarranged in the housing which drives the propeller shaft optionally bymeans of reduction gearing which may be configured in any conceivablemanner.

Surprisingly, it has been found that the jet pipe according to theinvention which is arranged at an angle demonstrates a very goodpropulsive effect, even if the peripheral edge of the inlet is onlyslightly below the surface of the water. Air which flows in is pressedagainst the inner wall of the jet pipe by means of the centrifugaleffect of the propeller, without the air bubbles which flow in enteringthe propeller and greatly reducing the efficiency of the propulsion.

The term “water-displacement” according to the invention is intended torefer to vessels having a Froude number which is less than 1, i.e.:F_(r)=V/(g·L)^(1/2)<1, where V is the velocity in m/s, g is thegravitational acceleration and L is the length of the vessel in m.

An embodiment of a water-displacement vessel according to the inventioncomprises an elongate hull which is provided with a front end and a rearend, wherein the pod is attached close to the rear end, wherein, in thecase of a low degree of loading, the peripheral edge is situated closeto or above the waterline in the rearward position and is situated adistance of at least in the order of 10% of the propeller diameter belowthe waterline in the forward position.

By reversing the orientation and the direction of rotation of the pod inthe case of a low degree of loading, the peripheral edge of the jet pipeis situated far enough below the surface of the water to realizeeffective propulsion. This enables sailing with a low draught withoutballast.

If, after a predetermined speed has been reached, a sufficient sternwave has built up that the pod is situated sufficiently far below thesurface of the water to ensure effective propulsion, the pod can berotated about the rotation shaft into the rearward position after apredetermined speed has been reached, with reversal of the direction ofrotation of the propeller. Preferably, the first axis is substantiallyparallel to the longitudinal axis in the rearward position.

According to a particular embodiment of the present invention, thesecond axis, i.e. the axis of rotation of the housing of the pod withrespect to the vessel, extends at an angle of 5-30° to the vertical.

In combination with the above-described angle of 60-80°, in theabove-described position rotated through 180°, starting from ahorizontal position at 0°, a displacement of 15-60° with respect to thehorizontal occurs. As a result, the propeller which is optionallyprovided with a jet pipe can be considerably limited in terms of height(depth).

According to a further advantageous embodiment of the invention, the podis arranged at the rear side of the hull of the vessel, which rear sideis slightly inclined with respect to the horizontal. In this case, it ispossible to arrange the rotation shaft, i.e. the second axis,perpendicularly to said inclined plane, as a result of which theabove-described deviation from the vertical is realized.

The displacement of the second axis with respect to the vertical iseffected preferably at least in the vertical central longitudinal planeof the vessel, which vertical central longitudinal plane of the vesselcomprises the longitudinal axis of the vessel. In other words, thesecond axis is preferably arranged at an incline with respect to thevertical in the forward or rearward direction with respect to thelongitudinal direction of the vessel.

It is also possible to displace said second axis, i.e. the axis aboutwhich the housing of the pod rotates, with respect to the vertical in adirection perpendicular to the longitudinal direction of the vessel.This is preferably realized in the case where two (or more) pods arepresent in a preferably symmetrical position with respect to thevertical central longitudinal plane.

According to a further advantageous embodiment of the present invention,an annular jet pipe is arranged around the propeller, said jet pipebeing provided at the top side with a (detachable) projection whichextends in the direction away from the housing and functions as a flowguide. The propeller is able to suck in water as soon as this projectionis submerged under water in the downwardly tilted position.

According to a further embodiment of the present invention, therotational movement of the second axis is more complex. In theembodiments described above, the second axis, i.e. the axis of rotationof the pod with respect to the vessel, is arranged in a fixed positionwith respect to the vessel.

According to a variant of the invention, this position of the secondaxis is varied depending on the rotation position with respect to thevessel. This may be realized by providing a bush in the vessel in whichthe pod may rotate about the second axis in the manner described above.However, said bush is itself rotatable about a third axis which deviatesfrom the second axis. By means of the mutual positioning of the rotationposition of the pod and the bush, a wide range of angles of thepropeller shaft, i.e. the first axis, may be realized.

The present invention also relates to a method for driving a vessel,which vessel comprises a hull, a pod, or thruster, which is rotatablewith respect to the hull and attached to the rear side under said hull,which pod comprises a housing which is rotatably attached to said hulland a driven propeller shaft arranged in said housing, which propellershaft protrudes through the housing and to which a propeller is attachedoutside the housing, wherein said pod serves to propel said vessel inboth sailing conditions and manoeuvring conditions, wherein said pod isrotated out of a sailing condition, in which the axis of said propellershaft is substantially horizontal, into a manoeuvring position, in whichthe axis of said propeller shaft forms an angle of 25-80° with respectto the horizontal.

In an embodiment in which the vessel is provided with at least two poddrives, at least one pod drive may be in the forward position, and theother in the rearward position. When sailing away at low speed, thepropeller of the pod in the rearward position may not be driven and thepod in the forward position can provide the propulsion by means of watersuction. If, after a predetermined speed has been reached, asufficiently large stern wave has built up, the rotation of thepropeller of the pod in the forward position may be ended and the pod inthe rearward position may assume the propulsion. The second pod may thenalso be rotated into the rearward position in order to assist with thepropulsion. This permits an efficient transfer of the propulsion fromthe pod in the forward position, without interruptions.

Apart from the situation described above, in which it is possible tostart up a vessel in a state in which it is not fully loaded withoutnegatively influencing the operation of the propeller, such a method mayalso be used for sailing in shallow water and other manoeuvres. It willbe understood that the construction according to the present inventionmay also optimally cover other operating conditions. For example, theinvention may be used for pontoons and other maritime structures whichmust remain in an accurately defined location. In the case of saidmaritime structures, the rearward position should be understood to meanthe main thrust direction in the case of a sufficient draught and theforward position in the case of a low draught. The same approach shouldbe used in the case of structures comprising a plurality of pods,possibly at the corners of the installation.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained in greater detail below with referenceto exemplary embodiments illustrated in the drawing, in which:

FIG. 1 diagrammatically shows a side view of a vessel in the loadedstate provided with the pod according to the invention in the rearwardposition;

FIG. 2 shows the vessel according to FIG. 1 in an entirely or partiallyempty state;

FIG. 3 shows the vessel according to FIG. 2 in an entirely or partiallyempty state, with the pod in the forward position,

FIG. 4 shows the vessel according to the present invention in anentirely or partially empty state once it has gained speed, with the podin the rearward position;

FIG. 5 shows details of the pod structure in the rearward position;

FIG. 6 shows the details according to FIG. 5, with the pod in theforward position;

FIGS. 7 a-d diagrammatically show top views and rear views of variouspositions of a variant comprising two pods; and

FIG. 8 shows a variant of the pod according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In FIG. 1, a vessel is designated overall by 1. According to the presentinvention, this is a relatively large vessel, such as an inland vessel,coaster or larger vessel. The length of the vessel is preferably greaterthan 20 or 40 metres. The driving power used for such vessels may, forexample, be in the range of many kilowatts to several megawatts. Thevessel is designated overall by 1 and is provided with a pod 2 at therear side which is designated by 3. The pod 2 comprises a jet pipe 17with an inlet delimited by a peripheral edge 11. The waterline in FIG. 1is indicated by 10 and the longitudinal axis of the hull is indicated by15. FIG. 1 illustrates the loaded state in which the propeller isentirely under the waterline.

FIG. 2 illustrates the same vessel 1 in an unladen state, in which thepod is attached in the manner customary in the prior art. It can be seenthat the pod, and in particular its propeller, and the inlet of the jetpipe 17 are above the waterline 10, as a result of which sailing is notreadily possible. The present invention proposes to tilt the pod and inparticular the axis of the propeller shaft and thus the propeller in themanner described below, as a result of which the same vessel asillustrated in FIG. 2, in the same loading state, can in fact now setsail, because the propeller is below the waterline level 10. This isillustrated in FIG. 3, in which the pod has been rotated through 180°and, as a result of the particular positioning thereof, the propellerand associated casing are below the waterline 10. In order to moveforwards, the direction of rotation of the propeller in the pod is ofcourse reversed, and the vessel can be set in motion.

As soon as the vessel has gained some speed, a stern wave will arise andas a result the propeller may be moved back into the usual position,i.e. with a substantially horizontal propeller shaft and a substantiallyvertical propeller plane. This is illustrated in FIG. 4, in which thepod once again has the usual direction of rotation.

FIG. 5 illustrates an exemplary embodiment in which it is possible torealize the tilting of the propeller illustrated in FIGS. 1-4 and moreparticularly in FIG. 3. A bearing bush 8 is arranged in the rear side 3of the vessel. The bearing bush 8 contains a pin 9 comprising an axis ofrotation (second axis) 12. In contrast to the prior art, said secondaxis 12 is not vertical, but deviates from the vertical, for example byan angle β of 5-30°. In the present example, this deviation occurssolely in the vertical central longitudinal plane which constitutes thelongitudinal axis 15 of the vessel. Depending on the incline of the rearside 3, it is possible to arrange the bearing bush 8 perpendicularly onsaid rear side. The other end of the pin 9 is connected to the housing 4of the pod 2. Said housing contains a propeller shaft 5 which protrudesthrough the housing 4 to the exterior and is connected to the propeller6. The axis of the propeller shaft is indicated by 7 and is designatedas the first axis. The jet pipe 17 comprising the inlet delimited by theperipheral edge 11 is arranged around the propeller. Said jet pipe 17may be provided at the top side with a (detachable) projection 13 whichextends away from the housing. The pod 2 may be provided with a drivewhich is situated in the ship's hull, in which case a drive shaft willextend through the pin 9. It is also possible to provide the pod 2 withan electrical drive which is situated in the housing 4. In that case,cabling will extend through the hollow pin 9. Other variants are alsopossible which are not illustrated in the drawing for the purpose ofemphasizing these different variant embodiments.

As shown in FIG. 5, the first axis 7 forms an angle, indicated by a,with the second axis 12, said angle being unequal to 90° and moreparticularly between 60-80°. In combination with the angle β, it ispossible to realize the position illustrated in FIG. 5, in which thepropeller shaft, i.e. the first axis 7, is substantially horizontal,i.e. is in an optimum position for driving the vessel over long periodsof time.

By rotating the pin 9, the pod housing will rotate along with thepropeller. A rotation through 180° will result in the situationillustrated in FIGS. 3 and 6. In that case, the propeller is at an angleto the horizontal, i.e. the first axis is no longer horizontal. Thissituation is somewhat less optimal for driving a vessel over largedistances. However, this situation does mean that the underside of thepropeller and of the jet pipe arranged around it is higher and the topside is lower. On the one hand, this provides the possibility of sailingin shallow water, and on the other hand it is possible, in the case of avessel which rides high, to first develop its speed. As described withreference to FIG. 4, it will subsequently be possible, as a result ofthe formation of a stern wave, to rotate the pod back into the positionin FIG. 5, in which case a sufficient amount of water will always bepresent to enable the problem-free operation of the propeller.

FIG. 5 further illustrates the intersection X between the propeller arcand the propeller shaft (or 1st axis) and the intersection Y between thepropeller shaft and the oblique rotation shaft (or 2nd axis). Thedistance between the two points (A) determines the geometric tilting andheight position of the propeller in the oblique downwards position. Ifthe value A=0, the propeller will tilt about point Y, which in this caseis the same as X, and the point X will not move vertically downwards andthe propeller will not protrude lower in the tilted position than in thehorizontal position. This selection for A applies in particular to shipswhich sail in shallow water (including inland vessels). If a greatervalue is chosen for A, for example values in the order of 50-100% of thepropeller diameter, the propeller will tilt about point Y and will bothtilt and move vertically downwards in the tilted position. Thisselection for A applies in particular to ships which sail with a lowdraught (including seagoing vessels).

FIG. 7 illustrates various operating states brought about by adjustingthe pod 2. FIG. 7 a illustrates a top view of a vessel, in which a podis arranged on either side of a central longitudinal axis 15. It ispossible to rotate these pods into a position of 90° as illustrated inFIG. 7 b or even to rotate them further into a position of, for example,120° as illustrated in FIG. 7 c. In these positions, it is possible tocarry out manoeuvres in slow sailing conditions or, in the case of fastsailing, to additionally achieve a braking effect.

FIG. 7 d illustrates a rear view of a vessel which shows that the secondaxes 12 are tilted with respect to the vertical in a plane which isperpendicular to the longitudinal axis 15. This tilting can be combinedwith the above-described tilting as illustrated in FIGS. 5 and 6.

FIG. 8 illustrates a further variant of FIGS. 5 and 6, wherein as far aspossible the same reference numerals have been used. In this case, thepin which is connected to the housing 4 of the pod is designated by 29and defines a second axis 32. Said pin is accommodated in a sleeve 30which is rotatable along a third axis 31 with respect to the stern of aship and for this purpose is mounted in a bearing bush 28. The secondand third axes diverge by an angle γ, as can be seen from the drawing.Mutual rotation about the second and third axes allows a wide range ofdifferent positions of the pod to be realized, as a result of which theabove-described effect of tilting the propeller can be even morepronounced and it is also possible, in the 0° or 180° position, forexample, to provide the housing of the pod with a different angle ofinclination. It is even possible to change the angle which the propellershaft forms with the horizontal by rotating the sleeve 30 whilst keepingthe pin 29 stationary.

1. Water-displacement vessel (1) comprising a hull with a longitudinalaxis (15), comprising a bottom and comprising a pod drive (2) arrangedclose to the bottom, said pod drive (2) being provided with a housing(4) containing a propeller shaft (5) which protrudes through the housingand to which propeller shaft (5) a propeller is attached at a propellerend, and a drive for said propeller shaft, which propeller shaft (5)defines a first axis (7), which housing (4) is rotatable with respect tothe hull between a rearward position and a forward position about arotation shaft (9, 29) which defines a second axis (12, 32) which is notvertical and forms an angle (α) of 40°-90°, preferably between 60°-80°,with the first axis, characterized in that an annular jet pipe (17) isarranged around the propeller, comprising a peripheral edge (11) whichis at a distance from the propeller shaft (5) and is situated furtherbelow a predetermined waterline in the forward position than in therearward position, wherein the direction of rotation of the propellershaft (5) in the forward position is adjustable in such a way that thejet pipe has a water-suction effect.
 2. Water-displacement vesselaccording to claim 1, comprising an elongate hull which is provided witha front end and a rear end, wherein the pod is attached close to therear end, wherein, in the case of a low degree of loading, theperipheral edge (11) is situated close to or above the waterline in therearward position and is situated a distance of at least in the order of10% of the propeller diameter below the waterline in the forwardposition.
 3. Water-displacement vessel according to claim 1, wherein thefirst axis (7) is substantially parallel to the longitudinal axis (15)in the rearward position.
 4. Water-displacement vessel according toclaim 1, wherein the pod is designed, in the case of a low degree ofloading, to drive the vessel in the forward position by means of suctionand, after a predetermined speed has been reached, to rotate about therotation shaft (9, 29) into the rearward position, with reversal of thedirection of rotation of the propeller.
 5. Water-displacement vesselaccording to claim 1 wherein the second axis (12, 32) forms an angle (β)of 5-30° with the vertical in the position of use.
 6. Water-displacementvessel according to claim 1, wherein the hull is inclined with respectto the horizontal at the location (3) where the pod (2) is attached tothe hull, and wherein the second axis (12) is perpendicular to the hullat the location of the attachment.
 7. Water-displacement vesselaccording to claim 1, wherein said hull comprises a vertical centrallongitudinal plane and said second axis (12) is situated in saidvertical central longitudinal plane or in a plane parallel thereto. 8.Water-displacement vessel according to claim 1, wherein said hullcomprises a vertical central longitudinal plane, two pods are present oneither side of said plane, wherein the second axes (12) of said pods arearranged mirror-symmetrically with respect to said vertical centrallongitudinal plane.
 9. Water-displacement vessel according to claim 8,wherein one pod can be moved into a rearward position while the otherpod is in a forward position.
 10. Water-displacement vessel according toclaim 8, wherein the second axes (12) are not in a plane parallel tosaid central longitudinal plane.
 11. Water-displacement vessel accordingto claim 1, wherein the jet pipe (17) is annular and is provided at atop side of a peripheral edge with a projection (13) which extends awayfrom said housing.
 12. Method for driving a water-displacement vessel(1) comprising a hull with a longitudinal axis (15), comprising a bottomand comprising a pod drive (2) arranged close to the bottom, said poddrive (2) being provided with a housing (4) containing a propeller shaft(5) which protrudes through the housing and to which propeller shaft (5)a propeller is attached at a propeller end, and a drive for saidpropeller shaft, which propeller shaft (5) defines a first axis (7),which housing (4) is rotatable with respect to the hull between arearward position and a forward position about a rotation shaft (9, 29)which defines a second axis (12, 32) which is not vertical and forms anangle (α) of 40°-90°, preferably between 60°-80°, with the first axis,wherein an annular jet pipe (17) is arranged around the propeller,comprising a peripheral edge (11) which is at a distance from thepropeller shaft, wherein the method comprises the following steps:rotating the housing about the rotation shaft into the forward position,and adjusting the direction of rotation of the propeller so that the jetpipe has a water-suction effect and the vessel is driven.
 13. Methodaccording to claim 12, wherein, after a predetermined speed has beenreached, the housing is rotated about the rotation shaft (9, 29) intothe rearward position, with reversal of the direction of rotation of thepropeller.
 14. Method according to claim 12, wherein the vessel isprovided with at least two pod drives (2), wherein at least one poddrive is situated in the forward position, and the other pod drive issituated in the rearward position.
 15. Method according to claim 12,wherein the vessel is substantially unladen.
 16. Method according toclaim 13, wherein the vessel is provided with at least two pod drives(2), wherein at least one pod drive is situated in the forward position,and the other pod drive is situated in the rearward position. 17.Water-displacement vessel according to claim 2, wherein the first axis(7) is substantially parallel to the longitudinal axis (15) in therearward position.
 18. Water-displacement vessel according to claim 2,wherein the pod is designed, in the case of a low degree of loading, todrive the vessel in the forward position by means of suction and, aftera predetermined speed has been reached, to rotate about the rotationshaft (9, 29) into the rearward position, with reversal of the directionof rotation of the propeller.
 19. Water-displacement vessel according toclaim 2, wherein the second axis (12, 32) forms an angle (β) of 5-30°with the vertical in the position of use.
 20. Water-displacement vesselaccording to claim 9, wherein the second axes (12) are not in a planeparallel to said central longitudinal plane.